Cytoplasmic male sterility (CMS) is a maternally transmitted trait, whereby a plant is unable to produce viable pollen. Studies have revealed that this trait is a tool for enabling efficient and reliable coexistence between genetically modified (GM) and non‐GM cultivation by biocontainment of GM maize (Zea mays L.) pollen. Maize has three types of male‐sterile cytoplasm (T, S, and C), the fertility of which can be restored by nuclear rf genes or by interactions with the environment. Twenty‐two CMS versions of modern European maize hybrids were evaluated in 17 environments in Switzerland, France, and Bulgaria, with two or three sowing dates, in 2005 and 2006. Stable and unstable male sterility occurred in all three CMS types. T‐cytoplasm hybrids were the most stable, while S‐cytoplasm hybrids often showed partial restoration of fertility. C‐cytoplasm was similar to T‐cytoplasm with regard to maintaining male sterility. Climatic factors, especially air temperature, evapotranspiration, and water vapor, during the 10 d before anthesis as well as during anthesis, were correlated positively or negatively with the partial reversion to male fertility of CMS hybrids, indicating an interaction between genetic and climatic factors. This study illustrates that T‐ and C‐cytoplasm in particular open up viable prospects for containing transgenic pollen, especially for Bt‐maize.

The implementation of modern inducer lines in maize breeding can substantially decrease the time required to create elite inbred lines. In industrialized countries, this method has already largely replaced conventional backcross methods. However, the application of in vivo gynogenesis for inducing doubled haploids is still limited to European and US maize germplasms and has still to be adapted for exotic plant material. The reliability of three modern European inducer lines from the University of Hohenheim (Germany) was investigated for the production of haploid progenies from subtropical specialty maize. Three Chinese hybrids heterozygous for waxy maize and opaque 2 were used as maternal donor material, as maize double recessive for waxy and opaque 2 may improve the nutrition of ethnic minorities in Southeast Asia. However, many false positives were detected by flow cytometry among putative haploid seeds based on anthocyanin pigmentation because the color expression was inhibited in almost 50% of the induced seeds from this maternal plant material. Based on flow cytometry, the haploid induction rates were high with 10.2-12.3%, and the chromosome doubling rates were around 50%; therefore the principal potential of producing DH was confirmed for subtropical maize. However inducer lines for the precise and fast recognition of truly induced haploid seeds still need to be developed.

Maize (Zea mays L.) Plus‐Hybrids are a blend of cytoplasmic male‐sterile (CMS) hybrids and unrelated male‐fertile hybrids ensuring pollination of the whole stand. Combining potential benefits of male sterility (CMS effect) and allo‐pollination (xenia effect), they often outperform the corresponding male‐fertile sib‐pollinated hybrids in terms of yield. The combining abilities of five CMS hybrids and eight pollinators were investigated in a factorial split‐plot design in 12 environments in four countries and two years. The plant material from different breeders represented the three types of male‐sterile cytoplasm. Plus‐Hybrids increased grain yield, on average, by 10% or more and by up to 20% in specific environments. Three highly responsive CMS hybrids and four generally good pollinators were identified. The Plus‐Hybrid effect affected both yield components, CMS leading mainly to a higher number of kernels (KN) and the xenia effect mainly to an increase in the thousand kernel weight (TKW). Despite some differences in the response of the three types of CMS, the effect of the cytoplasm was not significant. While the CMS effect depended strongly on environment, the xenia was consistent in all environments but its extent varied. As well as increasing yield, we can expect that Plus‐Hybrids can make a large contribution to the coexistence of transgenic and conventional maize by biocontainment, that is, eliminating or reducing the release of transgenic pollen in Bacillus thuringiensis (Bt) maize or herbicide‐tolerant (HT) maize.

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